1. Field of the Invention
The present invention generally relates to electron beam exposure devices, and more particularly, to a block type electron beam exposure device or a variable rectangular type electron beam exposure device, having a heat dissipating ability. By such electron beam exposure devices, an electron beam is formed into a beam having a rectangular cross-section by being passed through a slit assembly, and thus forms a beam which may be projected onto a wafer.
2. Description of the Related Art
Recently, demands have increased for an electron beam exposure device such as a precise forming of a LSI (large-scale integrated circuit) pattern which may reliably correspond to a fine structure of the LSI and a high-speed forming of the fine LSI pattern in order to improve a throughput of the circuit.
FIGS. 1A, 1B and 2 are diagrams showing a conventional first slit assembly 10 which is provided next to an electron gun in a conventional block type electron beam exposure device. FIG. 1A is a diagram showing a top view of the first slit assembly 10 and FIG. 1B is a diagram showing a cross-sectional view of the slit assembly 10. FIG. 2 is a diagram showing a cross-sectional view of a region of a stage of the first slit assembly 10 in a magnified scale.
As shown in these figures, the first slit assembly 10 used in a conventional block type electron beam exposure device is comprised of a housing 11, a base 12, a bearing 13, a stage 14, a slit member 16, worm gear 17, a motor 20, an exhaust port 21, and a cover 23.
The base 12 is fixed in the housing 11 and the stage 14 is rotatably supported by the base 12 with respect to a vertical axis 15 via the bearing 13. The slit member 16 is fixed on the stage 14 and the worm gear 17 is provided with the stage 14. The slit member 16 has a structure in which a plurality of slit forming members 26 are combined with each other so that a slit 25 having substantially a rectangular shape is formed in a center thereof. Each of the slit forming members 26 may be made of such metal as molybdenum having excellent thermal resistance.
The worm gear 17 may be comprised of a worm wheel 18, which is integrally formed with the stage 14, and a worm 19, which is supported by the base 12. The worm 19 is actuated by the motor 29 which is provided outside of the housing 11. The interior of the housing 11 may be maintained in a vacuum via the exhaust port 21. The slit member 16 is covered by the cover 23, which is fixed to the base 12, having a hole 22 at substantially the center thereof.
The electron beam irradiated from the electron gun passes through the hole 22 and reaches the slit 25 where a peripheral portion of the beam is blocked by the slit member 16. Thus, the electron beam which is passed through the slit 25 has a cross-section matched with the shape of the slit 25 (a rectangular shape in this case). The electron beam from the first slit assembly 10 having a cross-section of a rectangular shape may be projected onto a wafer through electromagnetic lenses and deflectors so that a LSI pattern is precisely formed on the wafer.
On the other hand, the reason that the stage 14 should be rotated with respect to the vertical axis 15 is that a phase of a second slit assembly (to be described later) is slightly rotated with respect to the electron beam whose cross-section is formed in a rectangular shape by the first slit assembly 10 due to the setting accuracy of the electromagnetic lens L1b or a subtle change in the strength of the electromagnetic lens Lb1 and it is necessary to carry out an adjustment operation corresponding to the above rotation. The adjustment, in which the stage 14 is rotated with respect to the vertical axis 15, may be made by appropriately operating the motor 20 before the irradiation of an electron beam so that the stage 14 is rotated, via the worm gear 17, in a range of a few degrees. In this manner, the parallelism and the vertical relationship of the electron beam passed through the first slit assembly 10 with respect to the sides of the second slit assembly may be adjusted within a predetermined range.
As mentioned above, when the cross-section of the electron beam is shaped into a rectangular form by the slit member 16, the peripheral portion of the electron beam is blocked by and irradiated onto the slit member 16. Thus, the temperature of the slit member 16 is increased by the electron beam. In order to lower the temperature of the slit member 16, the heat generated in the slit member 16 may be transferred to, in order, the stage 14, the base 12 and the housing 11.
However, as indicated by an arrow 30 in FIG.2, the heat transfer path from the stage 14 to the base 12 is narrowed by the plurality of balls of the bearing 13, whose contacting area is restricted (i.e., small) and unstable due to the circular shape thereof. Thus, the heat transfer efficiency from the stage 14 to the base 12 tends to become insufficient, and hence the temperature of the slit member 16 tends to be increased depending on the irradiation time and strength of the electron beam. If the temperature of the slit member 16 exceeds a certain limit, the slit member 16 may be melted or physically damaged, and hence a precise forming of a circuit pattern cannot be achieved by the slit member 16.
Also, because of this tendency of the slit member 16 to be heated to a high temperature, it is difficult to increase the strength of the electron beam in order to increase the speed of forming a circuit pattern using a conventional electron beam exposure device.
Moreover, when ozone gas is used to eliminate charge-up (or dust) in the column of the electron beam exposure device, the surface of the slit member 16 is easily oxidized upon contact with the ozone gas since the temperature of the slit member 16 is high. If the surface of the slit member 16 (the surface of the slit 25) is oxidized, the sides of the rectangular cross-section of the electron beam is no longer sufficiently straight, and hence a precision of a circuit pattern formed by the irradiation of the thus formed electron beam is lowered.
Further, the effect of a backlash associated with the worm gear 17 is likely to occur appeared as a slight shift in position of the stage 14 in the rotation direction. If the position of the stage 14 in the rotation direction is changed, an image projected onto a wafer through the slit is shifted in the rotation direction and a precision of a circuit pattern will also be decreased.